Heat protecting materials of the ablative type are known in the art. In contrast to regular heat insulating materials which afford heat protection due to their poor thermal conductivity, heat ablative materials provide thermal protection by absorbing heat, without a large increase of their temperature, for a limited period of time. Thus, in contrast to regular thermal insulating materials, heat ablative materials are for one time use. U.S. Pat. No. 4,462,831 to Raevsky et al. discloses a fire and heat protective material of the ablative type composed of an organic binder and a filler of hydrated aluminum sulfate.
Usually, heat ablative materials absorb heat due to endothermal reactions which take place upon heating. One such endothermal reaction is dehydration which is the loss of hydration water. In addition, other processes can contribute to the absorption of heat, such as the evaporation of the water molecules released in the dehydration reaction and the heating of any gases which are emitted during decomposition of the ablative material.
One type of heat ablative materials known in the art are hydrated inorganic salts. For example, gypsum which is calcium sulfate dihydrate (CaSO.sub.4.2H.sub.2 O), is a heat ablative material well known in the art. When gypsum is heated from 20.degree. C. to 1000.degree. C., it's temperature keeps nearly constant within the range of 100-104.degree. C. till the end of it's dehydration. After the dehydration is ended, gypsum substantially looses it's heat ablative property and the temperature increases quickly.
Heat ablative materials can be used for protection of heat sensitive materials such as ammunition, explosives, fuel and other combustible materials from exposure to intense heat. Such protection can be achieved by coating the container of the heat sensitive material with a layer of heat ablative material, or by storing heat sensitive materials and objects in a room or a case or a safe whose walls include a heat ablative material or are coated with a heat ablative material.
The efficiency of heat ablative compositions can be determined by measuring the time interval during which they can keep the temperature on one of their sides below a certain value while their other side is heated in a controlled way up to a certain predetermined temperature. This time interval is usually referred to as the time of heat protection.
Thus, heat ablative compositions having a long time of heat protection are desirable for providing extended heat protection periods.